Efficacy of turbulent convective heat transfer in a circular tube with water-based nanoemulsion of n–Eicosane–An experimental study

Abstract

The water-based microemulsion or nanoemulsion of phase change materials, that can be used as the dual functional thermal fluids for energy transport or/and energy storage, have received many attentions due to their practical applications in convective heat transfer improvement and thermal energy storage. This is owing to the advantages of these fluids in providing high effective specific heat resulted from latent heat release/absorption associated with freezing/melting behaviors within the phase change material particles. In general, it is important to evaluate the long-term overall energy efficiency of these fluids, used in thermal systems, under the practical and complex conditions. To address this issue, in the present study, the turbulent forced convective heat transfer of water-based nanoemulsion in a circular tube is experimentally investigated. The n-Eicosane, as a phase change material, with different mass fractions is suspended in the water by an ultrasonic-vibrator-aided emulsion process to prepare the nanoemulsion fluid. The circular tube is under a constant heat flux. The effects of different parameters, such as the Reynolds number, mass fraction of n-Eicosane particles, and heating power, on the dimensionless wall temperature, local convective heat transfer effectiveness, temperature control effectiveness, figure of merit (FOM), and pressure drop are studied. The experimental results reveal that the local convective heat transfer effectiveness decreases as the heating power increases. The use of n–Eicosane particles with smaller value of mass fraction can provide the convective heat transfer effectiveness larger than unity in the entire length of the heating section. The heating power has little effect on the pressure drop ratio. Increasing the heating power leads to a marginal decrease in the pressure drop ratio at larger values of the Reynolds number. The FOM index decreases as the mass fraction of n–Eicosane particles increases. The FOM index is decreased about 10% as the mass fraction of n–Eicosane particles increases in the range of 1% to 5% for the Reynolds number in the range of Re=4548∼4677. This decrease is 10.55% for the Reynolds number in the range of Re=5044∼5195. In addition, the FOM index is reduced with increasing the Reynolds number. The FOM index reduces about 1.3% as the range of Reynolds number increases from 4548∼4677 to 5044∼5195 for ωPCM=5%.